Field of the Invention
The present invention relates to an automatic transmission for vehicles, and more particularly, to a planetary gear train of an automatic transmission for vehicles capable of improving power transfer performance and fuel efficiency and securing linearity of an inter-stage part of a shift stage by increasing a span of a shift ratio while implementing advance (i.e., forward) 10-speeds by a minimum configuration.
Description of Related Art
Recently, increasing oil prices have caused vehicle manufacturers all over the world to rush into infinite competition. Particularly in the case of engines, manufacturers have been pursuing efforts to reduce the weight and improve fuel efficiency of vehicles by reducing engine size, etc.
As a result, research into reduction of weight and enhancement of fuel efficiency through downsizing has been conducted in the case of an engine and research for simultaneously securing operability and fuel efficiency competitiveness through multiple speed stages has been conducted in the case of an automatic transmission.
However, in the case of the automatic transmission, as the number of shift stages is increased, the number of internal components also increases, and as a result, the automatic transmission may be difficult to mount, the manufacturing cost and weight may be increased, and power transmission efficiency may be deteriorated.
Thus, in order to increase an effect of improving the fuel efficiency by the multi-stage transmission, it may be said that the development of a planetary gear train capable of maximizing efficiency with a small number of parts is important.
In this regard, an 8-speed automatic transmission has recently been implemented, and research and development into a planetary gear train capable of implementing a shift stage of 8-speed or more has been actively conducted.
However, in the case of the recent 8-speed automatic transmission, since a span of a shift ratio is maintained to a level of 6.5 to 7.5, the 8-speed automatic transmission does not have a great effect of improving the fuel efficiency.
As a result, in the case in which the span of the shift ratio of the 8-speed automatic transmission is set to a level of 9.0 or more, since linearity of an inter-stage ratio of a shift stage may not be secured, running efficiency of the engine and drivability of the vehicle are degraded. Therefore, there is a need to develop a high efficient automatic transmission of at least 9-speed or more.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.